Numerous dimensions of human health are beneficially influenced by physical activity, including neurological health. Multiple compelling lines of evidence indicate that physical activity, especially aerobic exercise, is a potent stimulus for neurogenesis, protecting new neurons, and boosting cognition and brain performance.
However, certain types of physical activity can also cause acute brain damage and possible neurodegenerative sequelae .
The most notable examples are sports that increase the risk of concussion and exposure to repetitive impacts to the head.
Sports neurologists therefore face an interesting puzzle: why is the human brain dependent on physical activity to function optimally and yet susceptible to damage from particular forms of athletics?
While knowledge of the mechanisms immediately responsible for a biological phenomenon is necessary to explain how that phenomenon exists, only evolutionary theory and data can explain why it exists. Therefore, it follows that a satisfactory scientific understanding of why sports activities are necessary and potentially dangerous for human brain health requires an evolutionary perspective.
The objective of this work is to provide answers to three questions. First, what type of physical activity are humans adapted for? Second, how have human brains co-evolved with physical activity patterns? And third, for what types of physical activity are human brains poorly or inadequately adapted?
| What types of physical activity are humans adapted to ? |
To show that humans are adapted for certain types of physical activity, it is useful to remember Darwin and his theory of natural selection.
Natural selection is the result of three phenomena: (1) all organisms have varying traits; (2) some of these traits are inherited; and (3) organisms compete for resources. Darwin’s profound intuition was that, over time, heritable traits that improve or hinder an organism’s ability to compete and produce offspring become more or less common across generations.
Many human adaptations are related to our ability to be physically active. Survival and reproductive success among humans, as in all animals, depends on the ability to move to obtain resources, find mates, and avoid predators. Natural selection has given rise to diverse patterns of physical activity among animals
Specifically, humans are well adapted for activities that require endurance rather than power and for activities that are rare or absent in other primates and mammals, such as the ability to walk and run long distances at relatively fast speeds in hot, arid conditions.
Humans’ unique physical activity patterns began once the human and chimpanzee lineages diverged from our last common ancestor between 8 and 5 million years ago. This species was a form of quadrupedal monkey that lived in the tropical forests of Africa. It was almost certainly well adapted for tree climbing, fighting, and other activities requiring power, but was less capable of endurance activities such as long-distance travel.
There is evidence that Australopithecus (7-4 million years old) were adapted for a combination of activities both on the ground and in trees, with their lower limbs showing key adaptations for bipedal walking, but their upper limbs retaining many useful features for climb. Although bipedalism in Australopithecus was probably not entirely human-like, natural selection apparently favored adaptations that allowed them to travel and obtain food more efficiently in open, non-forested habitats,
Homo erectus (3-2 million years old) was the oldest known ancestor with a body that was essentially human. Unlike Australopithecus, which retained adaptations for life in trees, H. erectus was a fully committed biped. It was the first species to practice a hunting and gathering lifestyle, this meant a heavy dependence on activities that require endurance, especially walking long distances. Today, few human groups continue to live by hunting and gathering, but those who do and who live in hot, arid Africa
Another fundamental adaptation of H. erectus was its ability for endurance running, most likely for hunting. The persistence of hunting is made possible by humans’ ability to run long distances at speeds that require quadrupedal mammals to gallop.
One of the advantages that humans have at this speed is the unique ability developed to cool the body by sweating.
All other mammals must cool themselves by panting, which they cannot do by galloping. Therefore, when chased for long periods, especially in hot conditions, animals will overheat and hide to cool down. Human hunters intermittently pursue their prey while running and then track them while walking; Eventually, the animals collapse from hyperthermia, at which point they become easy targets.
| How have human brains co-evolved with physical activity patterns? |
Although Australopithecus had slightly larger brains than chimpanzees, brain enlargement was pronounced in H. Erectus. Brains grew even larger in descendants, including H. neanderthalensis (1170–1740cm3) and modern humans, H. sapiens (1100–1900cm3). The coincidence between the initial peak in brain size in H. erectus and the emergence of adaptations for endurance and the hunter-gatherer lifestyle strongly suggests that these phenomena are evolutionarily linked.
The subsistence of hunter-gatherers critically depends on our unique and complex cognitive abilities. Among the most vital abilities is a greater ability to cooperate, which must have been enabled in H. erectus and more recent ancestors by brain expansion. To achieve this requires a brain equipped for cultural learning, in which a person’s social behavior is formed from information obtained from other members of the group.
Cultural learning, in turn, requires a fully developed theory of mind (the ability to understand the minds of others), the power to reason, the faculty of communicating through language and symbolic behavior, the means to realize a monitoring of complex social interactions and the means to curb selfish and aggressive impulses. All of these human cognitive abilities are absent or underdeveloped in other primates.
Hunting poses the additional and demanding cognitive challenge of having to anticipate the movement patterns of evasive and often cryptic prey, not only to locate the animal in the first place, but also to track it. Accomplishing these feats requires both inductive and deductive thinking: inductive logic to find and follow the animal based on clues from tracks, tracks, and other sights and smells, and deductive logic to form hypotheses about how the animal is likely to behave and use clues to test these predictions. The cognitive elements used in animal tracking may represent the roots of scientific thinking .
Although the neurophysiological underpinnings of humans’ motivation and propensity for certain types of physical activity are not fully understood, a crucial component is likely to be the brain’s natural reward circuitry . This highly sensitive system responds to stimuli generated by physical activity, especially aerobic exercise, and appears to play an important role in motivating people to be physically active and improve performance. Therefore, neurobiological rewards could be an important target for natural selection that favors particular patterns of physical activity, especially endurance-based activities.
| For what types of physical activity are human brains not well adapted? |
Although doctors may think of exercise as a strategy to prevent or help treat disease, evolutionary biologists think of physical activity as an ancient adaptation. From this perspective, until very recently, humans could never avoid physical activity; Therefore, human brains require it simply because we evolved to be physically active. The more interesting question is why human brains evolved to function so poorly without physical activity.
In the brain, increased levels of physical activity, especially aerobic exercise, result in increased production of neurotrophic factors which, in turn, increase neurogenesis, neuroprotection, and cognitive function.
The argument that human brains are maladapted to physically active but energy-limited individuals leads to the concept of maladjustment diseases . Maladjustments are diseases that are more common or serious today because our bodies and brains are poorly or inadequately adapted to modern environments.
The two main criteria to identify them are that:
(1) The disease is currently more common or more severe than among human populations in the past.
(2) Preventable determinants of disease have become more common in modern environments.
Several neurological and psychiatric diseases are good candidates for maladjustment diseases, especially those in which physical inactivity is a risk factor or can accelerate the disease, such as Alzheimer’s, Parkinson’s disease, multiple sclerosis, anxiety, and depression. . Gaining a better understanding of the neurological and mental health of living hunter-gatherers and other contemporary traditional-living non-industrialized populations should be a goal of future research.
An evolutionary perspective is also relevant to addressing why human brains are so susceptible to damage from particular activities that are common in some sports. Throughout evolutionary history, human skulls became increasingly fragile and prone to fractures.
Although the mechanisms responsible for this increase in skull fragility are not well understood, an important factor could be reduced androgen reactivity in modern humans, which may have been favored by natural selection because it facilitated hunting and hunting. collection by promoting social tolerance. Regardless of the causes, however, the consequence of this evolutionary change is that human brains are especially vulnerable to hemorrhages from skull fractures.
While humans are not the only animals susceptible to exposure to concussions or repetitive impacts to the head , the extraordinary expansion of the human brain throughout evolution has made it prone to damage from acceleration and deceleration forces. While this adaptation was vital for hunting and gathering, it came at the cost of a severely diminished ability to withstand accelerations and decelerations of the brain, which commonly occur among people participating in contact/collision sports.
| Conclusion |
Human brains require physical activity to function optimally because they evolved among our hunter-gatherer ancestors who were rarely able to avoid resistance-based exercise. Furthermore, because energy from foods was limited among our ancestors, they developed to require physical activity stimuli adjustable to demand capacity.
As a result, human brains are poorly adapted to the extreme physical inactivity typical of many people today, which in all likelihood contributes to the current high prevalence and severity of many neurological and mental health disorders. Thanks to our evolutionary history as physically active hunter-gatherers, human brains are adapted to derive significant health benefits from athletic activities, especially those involving aerobic exercise.
However, unfortunately exceptionally large human brains are also vulnerable to damage from certain sports, especially contact/collision sports, which increase the risk of concussion and repetitive exposure to head impacts.
